Office Complex

After exiting the elevator, break the grating on the wall near the floor. Don't go too close to the big electric wire -- see what it does to those poor headcrabs?

Inside the vent, crawl to the right. Bust the grating and be careful for more tongue monsters in the ceiling. Turn off the power by going through a door in the room and pressing a switch.

Then exit the room through the same doors which locked you out before. Walk by the now-powerless electrical wires and bust through the window.

First, go to the left and bust through a bunch of boxes with your crowbar. You'll find a shotgun, as well as a guard who is being ambushed by a mutant. Help him out with your newfound firepower -- he'll open the gate for you, and you can pick up some goodies.

Continue back and jump through a window into a room flooded with water. Don't touch the water -- it's electrified. Hop from table to table over to the power switch to kill the juice.

Whack open the grille in this room and jump into another ventilation shaft. You'll face some headcrabs and then a head-lopping fan (remember to duck).

You'll crumble the floor and fall into another room. Push the big and small crates so they're undernath a ladder up in the ceiling, then jump up from one to the other to the ladder. Crawl through, breaking vents along the way, but pause a moment before jumping out the last one. That scientist wasn't as cautious.

Jump out and take care of the security gun. You can get physical and take it on mano a mano with your pistol and shotgun, or you can deftly crawl underneath it and flip the switch to deactivate it.

Go up the stairs a few times. You'll come across a room with a boarded-up doorway. Break the planks and keep going.

You'll come to a giant meat locker. Open the door using the handle to the left. Inside, walk left and press a switch which will start a trolley above you that moves back and forth. Go back, climb a ladder, crawl around a bit, and then hop on the trolley when it comes past you. Then, smash the crates on the trolley and jump off the other side into another shaft.

Crawl through the shaft, jump up into another shaft, and continue until you jump out in front of a set of stairs.

Go up the stairs, and find the elevator shaft. You'll have to make a big leap across and grab onto the ladder on the other wall.

Edge around the shaft and keep climbing ladder. Poor scientist man.

Weird sight: watch what happens when the scientist hits the ground.

Once you're on top of the elevator, smash another grille and drop down inside. Use the flashlight to help you find the button.